The biggest thing Blm needs to overcome is the ability to cast fast because the second you sneeze and have to move, the entire spell is null and void. Personally, I go with SS, although the current gear choices leave you to simply taking what you can get until the next relic comes out. There used to be a thing for your relic where you can put certain stats on it, that's where the push for certain skills came into play.

I look at it like this, SS let you hit fast, get through the spell faster, and gives you that half a second to get the spell off before you have to move. It's also constant, unlike Crit, which hits whenever it feels like it, and determination just increases your overall damage. If you're deciding to do the zeta relic, I would suggest SS and Det, or SS and Crit. Otherwise, just push to 60 and get your OP gear.